This invention relates to a monopole antenna for wireless communication system, and more particularly to a simplified, small-sized monopole antenna.
A monopole antenna has the simplest structure and is used in various antenna systems, for example, an antenna system mounted on a vehicle. In general, an antenna system mounted on a vehicle also comprises a helical antenna as an antenna for a circularly polarized wave, in addition to a monopole antenna. In the antenna system, the helical antenna and the monopole antenna are arranged in parallel to each other, and are covered by a top cover.
In recent years, an antenna system is required to be small-sized, and accordingly, a monopole antenna also is desired to be small-sized. For example, the size and outward appearance of an antenna system mounted on a vehicle depends on the profile of the top cover of the antenna system. For the profile of the top cover to be small-sized, the physical height or length of the monopole antenna should be small or short.
The physical height or length of a monopole antenna is closely related to an antenna length of the monopole antenna. In addition, the antenna length of the monopole antenna must be in compliance with the reception wavelength. Therefore, it is difficult to simply shorten the physical height or length of the monopole antenna.
As is apparent from the above description, a need exists for a small-sized monopole antenna that considers the relationship between an antenna length and a reception wavelength.
In recent years, an antenna system is required to be small-sized, and accordingly, a monopole antenna also desired to be small-sized. For example, a size and an outward appearance of an antenna system mounted on a vehicle depend on the profile of the top cover of the antenna system. For the profile of the top cover to be small-sized, it is effective that a physical height or length of a monopole antenna be small or short.
The physical height or length of monopole antenna is closely related to an antenna length of the monopole antenna. In addition, the antenna length of the monopole antenna must be decided in compliance with the reception wavelength. Therefore, it is difficult to simply shorten the physical height or length of the monopole antenna.
As apparent from the above description, a need exists for a small-sized monopole antenna that considers the relationship between an antenna length and a reception wavelength.
The present invention provides a monopole antenna which is designed in consideration of the shorting effect of wavelength that wavelength of a wave is shortened when the wave propagates in dielectric in comparison with the case of the propagation wave in vacuum.
According to one aspect of the present invention, a method of designing a monopole antenna comprising a dielectric body and an antenna element is provided as the followings. Herein, the dielectric body has a predetermined relative dielectric constant as its characteristic, while the antenna element has a predetermined antenna length.
In the designing method according to one aspect of the present invention, a shortening coefficient of wavelength is calculated, corresponding to the predetermined relative dielectric constant of the dielectric body. Then the wavelength of a propagation wave, which is shortened in accordance with the shortening coefficient of wavelength, is specified. Furthermore, the predetermined antenna length is decided, so as to be proportional to the specified wavelength.
With the method mentioned above, the predetermined antenna length of the monopole antenna is shortened, and accordingly, the physical height or length of the monopole antenna becomes small or short.
In connection with the above-method, a monopole antenna described below is obtained as another aspect of the present invention.
The monopole antenna according to another aspect of the present invention comprises a dielectric body, an antenna element, and a ground plane conductor. The dielectric body has top and bottom surfaces and a first through hole formed between the top and bottom surface and communicating the top and bottom surfaces with each other. The dielectric body has a predetermined relative dielectric constant, as its characteristics. The antenna element is fitted into the first through hole. The antenna element has a predetermined antenna length that is proportional to a wavelength shortened in accordance with a shortening coefficient of wavelength corresponding to the predetermined relative dielectric constant of the dielectric body. The ground plane conductor has a second through hole and is fitted on the bottom surface of the dielectric body, so that the antenna element does not contact with the ground plane conductor.
A more complete understanding of the present invention, as well as further features and advantages of the present invention, will be obtained by reference to the following detailed description and drawings.